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new lint: iter_count
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‎CHANGELOG.md

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@@ -2134,6 +2134,7 @@ Released 2018-09-13
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[`invisible_characters`]: https://rust-lang.github.io/rust-clippy/master/index.html#invisible_characters
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[`items_after_statements`]: https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements
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[`iter_cloned_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_cloned_collect
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[`iter_count`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_count
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[`iter_next_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_loop
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[`iter_next_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_slice
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[`iter_nth`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_nth

‎clippy_lints/src/lib.rs

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@@ -774,6 +774,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&methods::INTO_ITER_ON_REF,
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&methods::ITERATOR_STEP_BY_ZERO,
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&methods::ITER_CLONED_COLLECT,
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&methods::ITER_COUNT,
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&methods::ITER_NEXT_SLICE,
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&methods::ITER_NTH,
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&methods::ITER_NTH_ZERO,
@@ -1576,6 +1577,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&methods::INTO_ITER_ON_REF),
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LintId::of(&methods::ITERATOR_STEP_BY_ZERO),
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LintId::of(&methods::ITER_CLONED_COLLECT),
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LintId::of(&methods::ITER_COUNT),
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LintId::of(&methods::ITER_NEXT_SLICE),
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LintId::of(&methods::ITER_NTH),
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LintId::of(&methods::ITER_NTH_ZERO),
@@ -1879,6 +1881,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&methods::FILTER_NEXT),
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LintId::of(&methods::FLAT_MAP_IDENTITY),
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LintId::of(&methods::INSPECT_FOR_EACH),
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LintId::of(&methods::ITER_COUNT),
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LintId::of(&methods::MANUAL_FILTER_MAP),
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LintId::of(&methods::MANUAL_FIND_MAP),
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LintId::of(&methods::OPTION_AS_REF_DEREF),

‎clippy_lints/src/methods/mod.rs

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@@ -1513,6 +1513,32 @@ declare_clippy_lint! {
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"replace `.bytes().nth()` with `.as_bytes().get()`"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for the use of `.iter().count()`.
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///
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/// **Why is this bad?** `.len()` is more efficient and more
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/// readable.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// // Bad
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/// let some_vec = vec![0, 1, 2, 3];
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/// let _ = some_vec.iter().count();
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/// let _ = &some_vec[..].iter().count();
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///
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/// // Good
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/// let some_vec = vec![0, 1, 2, 3];
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/// let _ = some_vec.len();
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/// let _ = &some_vec[..].len();
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/// ```
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pub ITER_COUNT,
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complexity,
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"replace `.iter().count()` with `.len()`"
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}
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pub struct Methods {
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msrv: Option<RustcVersion>,
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}
@@ -1558,6 +1584,7 @@ impl_lint_pass!(Methods => [
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MAP_FLATTEN,
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ITERATOR_STEP_BY_ZERO,
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ITER_NEXT_SLICE,
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ITER_COUNT,
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ITER_NTH,
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ITER_NTH_ZERO,
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BYTES_NTH,
@@ -1636,6 +1663,8 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
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lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
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},
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["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
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["count", "iter"] => lint_iter_count(cx, expr, &arg_lists[1], false),
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["count", "iter_mut"] => lint_iter_count(cx, expr, &arg_lists[1], true),
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["nth", "iter"] => lint_iter_nth(cx, expr, &arg_lists, false),
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["nth", "iter_mut"] => lint_iter_nth(cx, expr, &arg_lists, true),
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["nth", "bytes"] => bytes_nth::lints(cx, expr, &arg_lists[1]),
@@ -2588,6 +2617,39 @@ fn lint_iter_next<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, iter_
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}
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}
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fn lint_iter_count<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, iter_args: &'tcx [Expr<'tcx>], is_mut: bool) {
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let mut_str = if is_mut { "_mut" } else { "" };
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if_chain! {
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let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.typeck_results().expr_ty(&iter_args[0])).is_some() {
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Some("slice")
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} else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym::vec_type) {
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Some("Vec")
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} else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym!(vecdeque_type)) {
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Some("VecDeque")
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} else if match_trait_method(cx, expr, &paths::ITERATOR) {
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Some("std::iter::Iterator")
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} else {
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None
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};
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if let Some(caller_type) = caller_type;
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then {
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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ITER_COUNT,
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expr.span,
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&format!("called `.iter{}().count()` on a `{}`", mut_str, caller_type),
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"try",
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format!(
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"{}.len()",
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snippet_with_applicability(cx, iter_args[0].span, "..", &mut applicability),
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),
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applicability,
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);
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}
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}
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}
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fn lint_iter_nth<'tcx>(
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cx: &LateContext<'tcx>,
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expr: &hir::Expr<'_>,

‎tests/ui/auxiliary/option_helpers.rs

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@@ -48,4 +48,8 @@ impl IteratorFalsePositives {
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pub fn skip_while(self) -> IteratorFalsePositives {
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self
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}
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pub fn count(self) -> usize {
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self.foo as usize
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}
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}

‎tests/ui/iter_count.fixed

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@@ -0,0 +1,58 @@
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// run-rustfix
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// aux-build:option_helpers.rs
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#![warn(clippy::iter_count)]
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#![allow(unused_variables)]
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#![allow(unused_mut)]
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extern crate option_helpers;
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use option_helpers::IteratorFalsePositives;
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use std::collections::{HashSet, VecDeque};
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/// Struct to generate false positives for things with `.iter()`.
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#[derive(Copy, Clone)]
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struct HasIter;
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impl HasIter {
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fn iter(self) -> IteratorFalsePositives {
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IteratorFalsePositives { foo: 0 }
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}
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fn iter_mut(self) -> IteratorFalsePositives {
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IteratorFalsePositives { foo: 0 }
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}
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}
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fn main() {
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let mut some_vec = vec![0, 1, 2, 3];
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let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
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let mut some_vec_deque: VecDeque<_> = some_vec.iter().cloned().collect();
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let mut some_hash_set = HashSet::new();
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some_hash_set.insert(1);
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{
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// Make sure we lint `.iter()` for relevant types.
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let bad_vec = some_vec.len();
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let bad_slice = &some_vec[..].len();
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let bad_boxed_slice = boxed_slice.len();
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let bad_vec_deque = some_vec_deque.len();
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let bad_hash_set = some_hash_set.len();
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}
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{
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// Make sure we lint `.iter_mut()` for relevant types.
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let bad_vec = some_vec.len();
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}
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{
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let bad_slice = &some_vec[..].len();
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}
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{
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let bad_vec_deque = some_vec_deque.len();
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}
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// Make sure we don't lint for non-relevant types.
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let false_positive = HasIter;
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let ok = false_positive.iter().count();
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let ok_mut = false_positive.iter_mut().count();
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}

‎tests/ui/iter_count.rs

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@@ -0,0 +1,58 @@
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// run-rustfix
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// aux-build:option_helpers.rs
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#![warn(clippy::iter_count)]
5+
#![allow(unused_variables)]
6+
#![allow(unused_mut)]
7+
8+
extern crate option_helpers;
9+
10+
use option_helpers::IteratorFalsePositives;
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use std::collections::{HashSet, VecDeque};
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13+
/// Struct to generate false positives for things with `.iter()`.
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#[derive(Copy, Clone)]
15+
struct HasIter;
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17+
impl HasIter {
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fn iter(self) -> IteratorFalsePositives {
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IteratorFalsePositives { foo: 0 }
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}
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fn iter_mut(self) -> IteratorFalsePositives {
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IteratorFalsePositives { foo: 0 }
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}
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}
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fn main() {
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let mut some_vec = vec![0, 1, 2, 3];
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let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
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let mut some_vec_deque: VecDeque<_> = some_vec.iter().cloned().collect();
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let mut some_hash_set = HashSet::new();
32+
some_hash_set.insert(1);
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34+
{
35+
// Make sure we lint `.iter()` for relevant types.
36+
let bad_vec = some_vec.iter().count();
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let bad_slice = &some_vec[..].iter().count();
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let bad_boxed_slice = boxed_slice.iter().count();
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let bad_vec_deque = some_vec_deque.iter().count();
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let bad_hash_set = some_hash_set.iter().count();
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}
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{
44+
// Make sure we lint `.iter_mut()` for relevant types.
45+
let bad_vec = some_vec.iter_mut().count();
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}
47+
{
48+
let bad_slice = &some_vec[..].iter_mut().count();
49+
}
50+
{
51+
let bad_vec_deque = some_vec_deque.iter_mut().count();
52+
}
53+
54+
// Make sure we don't lint for non-relevant types.
55+
let false_positive = HasIter;
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let ok = false_positive.iter().count();
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let ok_mut = false_positive.iter_mut().count();
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}

‎tests/ui/iter_count.stderr

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@@ -0,0 +1,52 @@
1+
error: called `.iter().count()` on a `Vec`
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--> $DIR/iter_count.rs:36:23
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|
4+
LL | let bad_vec = some_vec.iter().count();
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| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec.len()`
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|
7+
= note: `-D clippy::iter-count` implied by `-D warnings`
8+
9+
error: called `.iter().count()` on a `slice`
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--> $DIR/iter_count.rs:37:26
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|
12+
LL | let bad_slice = &some_vec[..].iter().count();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec[..].len()`
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15+
error: called `.iter().count()` on a `slice`
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--> $DIR/iter_count.rs:38:31
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|
18+
LL | let bad_boxed_slice = boxed_slice.iter().count();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `boxed_slice.len()`
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error: called `.iter().count()` on a `VecDeque`
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--> $DIR/iter_count.rs:39:29
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|
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LL | let bad_vec_deque = some_vec_deque.iter().count();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec_deque.len()`
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27+
error: called `.iter().count()` on a `std::iter::Iterator`
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--> $DIR/iter_count.rs:40:28
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|
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LL | let bad_hash_set = some_hash_set.iter().count();
31+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_hash_set.len()`
32+
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error: called `.iter_mut().count()` on a `Vec`
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--> $DIR/iter_count.rs:45:23
35+
|
36+
LL | let bad_vec = some_vec.iter_mut().count();
37+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec.len()`
38+
39+
error: called `.iter_mut().count()` on a `slice`
40+
--> $DIR/iter_count.rs:48:26
41+
|
42+
LL | let bad_slice = &some_vec[..].iter_mut().count();
43+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec[..].len()`
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45+
error: called `.iter_mut().count()` on a `VecDeque`
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--> $DIR/iter_count.rs:51:29
47+
|
48+
LL | let bad_vec_deque = some_vec_deque.iter_mut().count();
49+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `some_vec_deque.len()`
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51+
error: aborting due to 8 previous errors
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